Phase Compensation For An Inductive Position Sensor

ABSTRACT

An interface circuit for a position sensor system including an oscillator generating an oscillation signal having a carrier frequency and a primary phase, a primary coil responsive to the oscillation signal, and a secondary coil electromagnetically coupled to the primary coil by a target and configured to generate a secondary signal having the carrier frequency and a secondary phase provides phase compensation. The interface circuit includes a sampling and conversion circuit configured to sample the secondary signal during sample periods and convert the secondary signal into a digital signal, a demodulator coupled to receive the digital signal and configured to demodulate the digital signal in order to generate a position signal indicative of a position of the target, a phase detector coupled to receive the position signal and configured to detect an alignment of the secondary phase with respect to the sample periods and generate a phase detector output signal indicative of whether the secondary phase is aligned with the sample periods, and a delay circuit responsive to the phase detector output signal and configured to apply a delay to the sampling and conversion circuit if the phase detector output signal indicates that the secondary phase is not aligned with the sample periods.

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD

This disclosure relates generally to inductive position sensors and,more particularly, to inductive position sensors having phasecompensation.

BACKGROUND

As is known, inductive position sensors generally include a primary, ortransmitting coil that generates a biasing field in response to anoscillation signal and one or more secondary, or receiving coilselectromagnetically coupled to the primary coil for generating one ormore secondary signals. The secondary signal can be processed to detecta position of a target arranged such that the coupling between theprimary and secondary coils is a function of the target position. Forexample, the target can be a ferrous core around which the primary andsecondary coils are wound. In general, the target position informationis amplitude modulated in the secondary signal that can be demodulatedsynchronously with respect to the primary oscillation in order toextract target position information. In one example configuration, twosecondary coils are arranged to generate respective secondary signalsthat contain amplitude modulated sine and cosine information that can beprocessed to determine target angle.

Various error sources, such as coil to target misalignment and resultingsignal offset and amplitude errors, can be compensated. Inductiveposition sensors are used in a wide variety of applications includingautomotive and industrial applications and may perform the role of amotor position sensor.

SUMMARY

Described herein is an interface circuit and an inductive positionsensor system containing the interface circuit in which phasecompensation is provided. Phase compensation is achieved by detecting aphase alignment of a secondary signal with respect to sample periods ofa sampling and conversion circuit and applying a delay to the samplingand conversion circuit based on the phase alignment detection. In thisway, demodulation is performed synchronously with respect to thedetected phase of the secondary signal (thus taking into account anyphase shift) rather than with respect to the primary oscillation inorder to permit accurate recovery of the target position. As a result,signal attenuation due to phase error (i.e., a difference between thephase of the primary, oscillation signal and the secondary signal) canbe reduced and/or eliminated thereby providing a position sensor systemwith lower noise and greater permissible mechanical tolerances.Furthermore, such phase compensation is performed by a control loopautomatically and continuously and is based on actual phase detection sothat the phase compensation provides optimal results as phase shiftschange over temperature, lifetime, and installation tolerances.

According to the disclosure, a position sensor system includes anoscillator configured to generate an oscillation signal having a carrierfrequency and a primary phase, a primary coil coupled to receive theoscillation signal, a secondary coil electromagnetically coupled to theprimary coil and configured to generate a secondary signal having thecarrier frequency and a secondary phase. A sampling and conversioncircuit is configured to sample the secondary signal during sampleperiods and convert the secondary signal into a digital signal and ademodulator coupled to receive the digital signal is configured todemodulate the digital signal in order to generate a position signalindicative of the position of the target. A phase detector coupled toreceive the position signal is configured to detect an alignment of thesecondary phase with respect to the sample periods and generate a phasedetector output signal indicative of whether the secondary phase isaligned with the sample periods. A delay circuit responsive to the phasedetector output signal is configured to apply a delay to the samplingand conversion circuit if the phase detector output signal indicatesthat the secondary phase is not aligned with the sample periods.

Features may include one or more of the following individually or incombination with other features. The demodulator can include amultiplier configured to multiply the digital signal by a square-wavesignal, wherein the square-wave signal has a phase that is aligned withthe primary phase. A phase-locked loop can be configured to generate thesquare-wave signal. The square-wave signal can have a frequency of atleast four times the carrier frequency. The phase detector output signalcan indicate that the secondary phase is not aligned with the sampleperiods if an amplitude of a current sample of the position signal doesnot match an amplitude of a previous sample of the position signal. Thesecondary coil can include a first secondary coil and a second secondarycoil, wherein the first secondary coil is configured to generate a firstsecondary signal containing first amplitude modulated information andthe second secondary coil is configured to generate a second secondarysignal containing second amplitude modulated information that isninety-degrees out of phase with respect to the first amplitudemodulated information.

Also described is an interface circuit for a position sensor systemincluding an oscillator generating an oscillation signal having acarrier frequency and a primary phase, a primary coil responsive to theoscillation signal, and a secondary coil electromagnetically coupled tothe primary coil by a target and configured to generate a secondarysignal having the carrier frequency and a secondary phase. The interfacecircuit can include a sampling and conversion circuit configured tosample the secondary signal during sample periods and convert thesecondary signal into a digital signal and a demodulator coupled toreceive the digital signal and configured to demodulate the digitalsignal in order to generate a position signal indicative of a positionof the target. A phase detector coupled to receive the position signalis configured to detect an alignment of the secondary phase with respectto the sample periods and generate a phase detector output signalindicative of whether the secondary phase is aligned with the sampleperiods. The interface circuit can further include a delay circuitresponsive to the phase detector output signal and configured to apply adelay to the sampling and conversion circuit if the phase detectoroutput signal indicates that the secondary phase is not aligned with thesample periods.

Features may include one or more of the following individually or incombination with other features. The demodulator can include amultiplier configured to multiply the digital signal by a square-wavesignal, wherein the square-wave signal has a phase that is aligned withthe primary phase. A phase-locked loop can be configured to generate thesquare-wave signal. The square-wave signal can have a frequency of atleast four times the carrier frequency. The phase detector output signalcan indicate that the secondary phase is not aligned with the sampleperiods if an amplitude of a current sample of the position signal doesnot match an amplitude of a previous sample of the position signal. Thesecondary coil can include a first secondary coil and a second secondarycoil, wherein the first secondary coil is configured to generate a firstsecondary signal containing first amplitude modulated information andthe second secondary coil is configured to generate a second secondarysignal containing second amplitude modulated information that isninety-degrees out of phase with respect to the first amplitudemodulated information.

According to a further aspect of the disclosure, an interface circuitfor a position sensor system includes means for sampling the secondarysignal during sample periods and converting the secondary signal into adigital signal, means for processing the digital signal to generate aposition signal indicative of a position of the target, means fordetecting an alignment of the secondary phase with respect to theprimary phase based on the position signal, and means for applying adelay to the sampling and converting means if the secondary phase is notaligned with the sample periods. In embodiments, the alignment detectingmeans can include means for determining if an amplitude of a currentsample of the position signal matches an amplitude of a previous sampleof the position signal.

Also described is a method for detecting a position of a target in aposition sensor system having an oscillator generating an oscillationsignal having a carrier frequency and a primary phase, a primary coilresponsive to the oscillation signal, and a secondary coilelectromagnetically coupled to the primary coil and configured togenerate a secondary signal having the carrier frequency and a secondaryphase. The method can include sampling the secondary signal duringsample periods, converting the sampled secondary signal into a digitalsignal, demodulating the digital signal to generate a position signalindicative of the position of the target, detecting an alignment of thesecondary phase of the position signal with respect to the primary phaseof the oscillation signal to generate a phase detector output signalindicative of whether the secondary phase is aligned with the sampleperiods, and delaying the sampling and conversion of the secondarysignal if the secondary phase is not aligned with the sample periods.

Features may include one or more of the following individually or incombination with other features. Demodulating the digital signal caninclude multiplying the digital signal by a square-wave signal, whereinthe square-wave signal has a phase that is aligned with the primaryphase. The square-wave signal can be generated by a phase-locked loopand can have a frequency of at least four times the carrier frequency.The phase detector output signal can indicate that the secondary phaseis not aligned with the sample periods if an amplitude of a currentsample of the position signal does not match an amplitude of a previoussample of the position signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the disclosure, as well as the disclosureitself may be more fully understood from the following detaileddescription of the drawings, in which like reference numerals identifysimilar or identical elements:

FIG. 1 is a block diagram of an inductive position sensor systemincluding a position sensor interface with phase compensation accordingto the disclosure;

FIG. 2 shows example secondary signal waveforms associated with theinductive position sensor system of FIG. 1 both with and without phaseerror;

FIG. 3 shows an example secondary signal waveform with phase error andthe resulting sampled and digitized signal with phase compensationperformed by the position sensor system of FIG. 1 and also without phasecompensation applied;

FIG. 3A shows an example secondary signal waveform with phase error andthe resulting demodulated signal with phase compensation performed bythe position sensor system of FIG. 1 and also without phase compensationapplied;

FIG. 4 is a flow diagram illustrating a phase alignment detectionportion of secondary signal processing in the sensor system of FIG. 1;and

FIGS. 5 and 5A show a further block diagram of the position sensorinterface of FIG. 1.

DETAILED DESCRIPTION

Before describing the present disclosure, some introductory concepts andterminology are explained.

As used herein, the term “processor” or “controller” is used to describean electronic circuit that performs a function, an operation, or asequence of operations. The function, operation, or sequence ofoperations can be hard coded into the electronic circuit or soft codedby way of instructions held in a memory device. A “processor” canperform the function, operation, or sequence of operations using digitalvalues or using analog signals. In some embodiments, the “processor” canbe embodied in an application specific integrated circuit (ASIC), whichcan be an analog ASIC or a digital ASIC. In some embodiments, the“processor” can be embodied in a microprocessor with associated programmemory. In some embodiments, the “processor” can be embodied in adiscrete electronic circuit, which can be an analog or digital. Aprocessor can contain internal processors or internal modules thatperform portions of the function, operation, or sequence of operationsof the processor. Similarly, a module can contain internal processors orinternal modules that perform portions of the function, operation, orsequence of operations of the module.

While electronic circuits shown in figures herein may be shown in theform of analog blocks or digital blocks, it will be understood that theanalog blocks can be replaced by digital blocks that perform the same orsimilar functions and the digital blocks can be replaced by analogblocks that perform the same or similar functions. Analog-to-digital ordigital-to-analog conversions may not be explicitly shown in thefigures, but should be understood.

In particular, it should be understood that a so-called comparator canbe comprised of an analog comparator having a two state output signalindicative of an input signal being above or below a threshold level (orindicative of one input signal being above or below another inputsignal). However, the comparator can also be comprised of a digitalcircuit having an output signal with at least two states indicative ofan input signal being above or below a threshold level (or indicative ofone input signal being above or below another input signal),respectively, or a digital value above or below a digital thresholdvalue (or another digital value), respectively.

As used herein, the term “predetermined,” when referring to a value orsignal, is used to refer to a value or signal that is set, or fixed, inthe factory at the time of manufacture, or by external means, e.g.,programming, thereafter. As used herein, the term “determined,” whenreferring to a value or signal, is used to refer to a value or signalthat is identified by a circuit during operation, after manufacture.

Referring to FIG. 1, an inductive position sensor system 10 configuredto sense a position of a target 14 includes an oscillator 18 to generatean oscillation signal 20 having a carrier frequency and a primary phase,a primary coil 22 coupled to receive, or transmit the oscillationsignal, and a secondary coil 26 electromagnetically coupled to theprimary coil 22 and configured to generate a secondary signal 24 havingthe carrier frequency and a secondary phase. The coupling between theprimary and secondary coils 22, 26 is a function of the target position.In an example embodiment, the target 14 is a metallic, non-ferromagneticobject and the primary coil 22 induces eddy currents in the target,which eddy currents, in turn induce a signal (i.e., the secondary signal24) in the secondary coil 26. As the target 14 moves (e.g., rotates),the coupling between the primary winding 22 and the secondary winding 26changes, so as to thereby encode target position information by way ofamplitude modulation of the secondary signal 24. It will be appreciatedthat various mechanical configurations for the target 14 and primary andsecondary coils 22, 26 are possible.

A position sensor interface circuit 28 includes a sampling andconversion circuit 30 configured to sample the secondary signal 24during sample periods and convert the secondary signal into a digitalsignal 32 and a demodulator 44 coupled to receive the digital signal 32and configured to demodulate the digital signal in order to generate ademodulated position signal 48 indicative of the position of the target14. A phase detector 34 coupled to receive the position signal 48 isconfigured to detect an alignment of the secondary phase with respect tothe sample periods and generate a phase detector output signal 36indicative of whether the secondary phase is aligned with the sampleperiods. A delay circuit 40 is responsive to the phase detector outputsignal 36 and configured to update an internally stored delayapproximation based on the value of the phase detector signal 36 and toapply a delay to the sampling and conversion circuit 30 if the phasedetector output signal 36 indicates that the secondary phase is notaligned with the sample periods (or, in other words, if the phasedetector output signal 36 indicates that the output of the delay circuit42 is not aligned with the secondary phase).

With this arrangement, inaccuracies in position sensing due to phaseerror (i.e., a difference between the phase of the oscillation signal 20and the phase of the secondary signal 24) are reduced and/or eliminated.Phase error can manifest as attenuation of the demodulated positionsignal 48. Thus, by providing phase error compensation, the positionsensing system 10 can achieve lower noise performance and permit greatermechanical tolerances.

Sampling and conversion circuit 30 functions to integrate the secondarysignal 24 over sample periods or windows to generate digital signal 32.It will be appreciated however, that other types of sampling andconversion circuits are possible, such as discrete time samplingcircuits.

Referring also to FIG. 2, plots 204, 214 show example secondary signalwaveforms associated with the inductive position sensor system 10 ofFIG. 1. Plots 204, 214 have a horizontal axis with a scale in arbitraryunits of time and a vertical axis with a scale in normalized units ofvoltage. Time intervals T1-T4 represent sample periods associated withthe sampling and conversion circuit 30. Example secondary signal 208,that may be the same as or similar to signal 24 of FIG. 1, does not haveany phase error with respect to oscillation signal (i.e., there is phasealignment between the oscillation signal 20 and the secondary signal208) and example secondary signal 218, that may be the same as orsimilar to signal 24 of FIG. 1, has a phase error with respect to theoscillation signal 20 (i.e., there is a phase difference, or shiftbetween the oscillation signal 20 and the secondary signal 218).

Consideration of phase-aligned secondary signal 208 reveals that thissinusoidal signal is centered on the sample periods T1-T4 in the sensethat its maxima peaks and minima valleys coincide with sample periodboundaries. Phase-shifted secondary signal 218 on the other hand is notcentered with respect the sample periods T1-T4. It will be appreciatedthat integration of phase-aligned signal 208 over sample periods T1-T4(as may be performed by sampling and conversion circuit 30) would resultin a square-wave digital signal (as will be illustrated in FIG. 3A)since, during each two consecutive sample periods, the signal 208 isequal in magnitude and opposite in polarity with respect to the signalduring the next two consecutive sample periods. For example, integrationof signal 208 over sample periods T1 and T2 provides a result having anequal magnitude and opposite polarity with respect to integration ofsignal 208 over sample periods T3 and T4. Whereas integration ofphase-shifted signal 218 on the other hand would result in a morediscontinuous signal, for example as may have time delays betweenintegration periods (as will be illustrated in FIG. 3A). This isillustrated by considering that integration of signal 218 over sampleperiods T1 and T2 does not provide a result that is equal in magnitudeand opposite in polarity with respect to integration over sample periodsT3 and T4.

Referring also to FIG. 3, a plot 300 shows an example secondary signalwaveform 304 having a phase error with respect to the carrier frequency,a sampled and converted version 312 of the secondary signal 304 as wouldresult if phase compensation were not applied (i.e., if the phasedetector 34 and delay circuit 40 were not used), and a sampled andconverted version 318 of the secondary signal 304 illustrating operationof the inductive position sensor system of FIG. 1 in which phasecompensation is applied by the control loop including the phase detector34 and delay circuit 40. Plot 300 has a horizontal axis with a scale inarbitrary units of time and a vertical axis with a scale in normalizedunits of voltage. Secondary signal 304 can be the same as or similar tosecondary signal 24 of FIG. 1 or signal 218 of FIG. 2 and has a phaseerror with respect to the primary signal (i.e., secondary signal 304 hasa phase error with respect to the carrier frequency of the primarysignal). Consideration of signal 318 reveals a square-wave signal sincethe sample windows over which the received signal 304 is sampled anddigitized coincide with symmetrical portions of the received signal 304;whereas consideration of signal 312 reveals a more discontinuous signalsince, without the described phase compensation applied, the samplewindows over which the received signal 304 is sampled and digitized donot coincide with symmetrical portions of the received signal 304.

Referring also to FIG. 3A, a plot 320 again shows example secondarysignal waveform 304 having a phase error with respect to the carrierfrequency, here along with a demodulated signal 332 that would resultfrom demodulating signal 312 if phase compensation were not applied(i.e., if the phase detector 34 and delay circuit 40 were not used), anda demodulated signal 348 achieved by demodulating signal 318illustrating operation of the inductive position sensor system of FIG. 1in which phase compensation is applied by the control loop including thephase detector 34 and delay circuit 40. Plot 320 has a horizontal axiswith a scale in arbitrary units of time and a vertical axis with a scalein normalized units of voltage. Demodulated signal 332 illustratesdemodulation of signal 312 without phase compensation aspects of thedisclosure applied (i.e., without use of the control loop includingphase detector 34 and delay circuit 40) and thus does not correspond toany signals of FIG. 1. Demodulated signal 348 illustrates demodulationof signal 318 by operation of the interface 28 in applying phasecompensation and thus, can be the same as or similar to demodulatedposition signal 48 (FIG. 1).

Consideration of demodulated signal 312 reveals that demodulating aphase shifted received signal (e.g., signal 304) without phasecompensation applied yields a signal having an alternating pattern.Phase detector 34 (FIG. 1) operates to detect whether or not thedemodulated signal is phase-aligned with the oscillation signal 20 andgenerate a phase detector output signal 36 accordingly.

A phase-locked loop (PLL) 50 can be used to generate a signal for use bydemodulator 44 in order to extract, or recover target positioninformation from the digital signal 32. More particularly, PLL 50 can becoupled to the oscillator 18 and to a frequency multiplier 52 andprovide a frequency locked signal to such elements 18, 52. Multiplier 52can generate a square-wave signal having a frequency that is a multipleof the carrier frequency of the oscillation signal 20.

Delay circuit 40 functions to apply a delay to the square-wave signalfrom the multiplier 52 if the phase detector output signal 36 indicatesthat the secondary phase is not aligned with the sample periods in orderto thereby generate a square-wave signal 42 for use by demodulator 44.Thus, the square-wave signal provided by the multiplier 52 can beprocessed by the delay circuit 40 in order to generate a demodulatingsquare-wave signal 42 that is phase-aligned with respect to theoscillation signal 20.

Demodulator 44 is configured to multiply the digital signal 32 by thesquare-wave signal 42 in order to generate the demodulated positionsignal 48. It will be appreciated by those of ordinary skill in the artthat other demodulation circuitry and methodologies can be used, such asdividing the digital signal 32 by the oscillation signal 20 for example.

The alternating pattern of a demodulated secondary signal that exhibitsphase error with respect to the oscillation signal can be used to detecta phase misalignment between the secondary signal 24 and the oscillationsignal 20. For this reason, the frequency of the square-wave signal 42is at least four times the frequency of the oscillation signal 20. Thisis because, if the square-wave signal 42 were less than four times thefrequency of the oscillation signal 20, then an alternating patternwould not occur, and the phase misalignment could not be detected in themanner described below.

Phase alignment detection can be accomplished by comparing consecutivesamples of the demodulated position signal 48. In particular, the phasedetector output signal 36 can indicate that the secondary phase (i.e.,phase of the secondary signal 24) is not aligned with the sample periodsif an amplitude of a current sample of the demodulated position signal48 does not match an amplitude of a previous sample of the demodulatedposition signal. An amplitude difference between consecutive samples ofthe demodulated position signal 48 indicates whether the applied delayis greater than or less than the actual delay between the primary signaland the secondary signal. The difference in phase between the primarysignal and the secondary signal is indicated by the amount of delayapplied by the delay circuit 40.

It is because of the increased sampling rate (i.e., at least four timesthe carrier frequency) that yields the alternating pattern in thedemodulated signal 48 and thus, that permits use of this advantageousmethod of comparing consecutive samples in order to determine the phasealignment. It will be appreciated by those of ordinary skill in the artthat a sampling rate of greater than four times the carrier frequencymay be used as it would still allow for the phase error and positioninformation to be independently recovered; however, because the phaseerror would no longer have a simple alternating pattern, a more complexpattern (based at least in part on the sampling rate and carrierfrequency) would need to be detected in the demodulated signal 48.

In some embodiments, the message bandwidth (i.e., the envelope of theamplitude modulated secondary signal 24) can be small with respect tothe carrier frequency (i.e., the frequency of the oscillation signal 20)in order for the difference between consecutive samples to accuratelyreflect the phase error.

The delay circuit 40 is coupled to receive the phase detector outputsignal 36 and is configured to introduce a delay to the sampling andconversion circuit 30 if the signal 36 indicates a phase misalignment.In some embodiments, signal 36 provides an indication of the phase shiftbetween the digital signal 32 and the oscillation signal 20 and thedelay introduced by the delay circuit 40 corresponds to the amount ofthe detected phase shift. For example, the introduced delay can be adelay or shift of the sample periods (e.g., periods T1-T4 in FIG. 2) andthe phase shift indicated by signal 36 (i.e., the value of the signal36) can determine the amount by which the sample periods are shifted.

In this way, the delay circuit 40 operates to align the demodulationphase by setting up the sample windows to account for any phase shiftbetween the secondary signal 24 and the oscillation signal 20. Stateddifferently, demodulation is performed synchronously with respect to thedetected phase of the secondary signal (thus taking into account anyphase shift) rather than with respect to the primary oscillation inorder to accurately recover target position information.

Further, the control loop including the sampling and conversion circuit30, the phase detector 34 and the delay circuit 40 operate continuouslyto adjust the sample window delay in the sampling and conversion circuit30 in order to minimize the phase related error. Phase compensation bythe described control loop is performed automatically and continuouslyand is based on actual phase detection (rather than an estimate of phaseerror for example) so that the phase compensation provides optimalresults as phase shifts change over temperature, lifetime, andinstallation tolerances.

Referring also to FIG. 4, a flow diagram illustrates a process 400 fordetecting whether or not the demodulated signal 48 is phase-aligned withrespect to the oscillation signal 20. The process commences at block 404with the demodulated signal 48 being sampled (e.g., by the sampling andconversion circuit 30) at a frequency of at least four times the carrierfrequency (i.e., the frequency of the oscillation signal 20).

At decision block 408, the current sample is compared to a last (i.e., aconsecutively previous) sample. If it is determined that the amplitudeof the current sample is the same as the amplitude of the last sample,then block 404 is repeated and the demodulated signal 48 is againsampled, as shown. Thus, blocks 404 and 408 are repeated as long as eachsample has the same amplitude as the last sample.

If however it is determined at block 408 that the amplitude of thecurrent sample is not the same as the amplitude of the last sample, thenthe delay circuit 40 (FIG. 1) introduces a delay to the sampling andconversion circuit 30 at block 412, which delay may be based on theextent to which the amplitude of the current sample and last samplediffer.

It will be appreciated that other circuitry and methodologies arepossible for detecting phase alignment of the demodulated signal 48 withrespect to the oscillation signal 20. For example, simple carrier phaserecovery such as using a single zero crossing comparator could be usedto measure the phase of the secondary signal 24; however, the resultingaccuracy may be limited due to offsets and offset drift.

Referring also to FIGS. 5 and 5A, an inductive position sensor system500 can be an implementation of the system 10 of FIG. 1. To this end,system 500 includes an oscillator, a primary coil 522, here twosecondary coils 524, 526, and an interface circuit 518. Interfacecircuit 518 generates an oscillation signal for coupling to primary coil522 through connections 530, 532 and is coupled to receive secondarysignals from secondary coils 524, 526 through respective connections534, 536, and 538, 540, as shown. Secondary coils 524, 526 areelectromagnetically coupled to the primary coil 522 and mechanicallycoupled to a target 520 such that movement of the target causes positioninformation to be encoded in the secondary signals from coils 524, 526by amplitude modulation.

The oscillator 528 may take the form of the illustrated resonant circuit(e.g., an LC tank circuit including capacitors 528 and primary coil 522)or other oscillation circuits. As explained above, the oscillationsignal has a carrier frequency and a primary phase and the secondarysignal, here signals, have the carrier frequency and a respectivesecondary phase.

Secondary windings 524, 526 can be designed to have a predeterminedphase relationship with respect to each other in order to suit aparticular application. In the example embodiment, secondary windings524, 526 are designed to generate respective secondary signals inquadrature (i.e., having a nominal ninety-degree phase shift withrespect to each other). With this arrangement, the system 500 cangenerate quadrature sine and cosine output signals (at connections 592,594 and 596, 598) that can be used to determine target speed, direction,and/or angle.

In some embodiments, multiple secondary signals have the same phaseshift with respect to the primary and thus, phase error compensation canbe achieved with a single control loop including the phase detector 34and delay circuit 40. In other embodiments however, it may be desirableto provide multiple control loops, each dedicated to a differentsecondary signal.

Interface 518 can include two signal paths (e.g., an analog, digital ormixed signal path) each coupled to receive a secondary signal from asecondary winding 524, 526. Each signal path can include an EMI filter552, 554 and an analog-to-digital converter (ADC) 556, 558 as shown.ADCs 556, 558 can be the same as or similar to sampling and conversioncircuit 30 (FIG. 1) and thus, can be configured to sample the respectivesecondary signal (e.g., by integration over sample periods) and convertthe integrated signal into a digital signal in order to generate adigital signal 546 that can be the same as or similar to digital signal32 (FIG. 1).

Oscillator driver 550 contains a demodulator, that may be the same as orsimilar to demodulator 44 of FIG. 1, and phase error compensationcontrol loop elements, that may be the same as or similar to phasedetector 34, delay circuit 40, PLL 50, and frequency multiplier 52 (FIG.1). Thus, oscillator driver 550 is configured to detect an alignment ofthe secondary phase with respect to the primary phase (based onobservation of the demodulated signal) and apply a delay to the ADCs556, 558 if the secondary phase is not aligned with the sample periods(i.e., the output of the delay circuit 40 is not aligned with thesecondary phase). In this way, oscillator driver 550 operates to alignthe demodulation phase by setting up the sample windows to account forany phase shift between the secondary signals and the oscillationsignal. Thus, demodulation is performed synchronously with respect tothe detected phase of the secondary signals (thus taking into accountany phase shift) rather than with respect to the primary oscillation inorder to accurately recover target position information.

The signal paths may further include various signal conditioning andcompensation of possible errors due to coils-target alignments andsystem design. For example, amplitude and offset adjustment may beprovided by circuits 562, 564. In general, signal amplitudes will beaffected by the current flowing through the primary coil 522 and thedistance between the coil and the target. Temperature may also affectsignal amplitudes and offsets. Thus, amplitude and offset adjustmentcircuits 562, 564 can be coupled to receive temperature information froma temperature sensor 560 and can operate to automatically track andcompensate signal amplitudes and offsets. Harmonic compensators 566, 568can perform compensation on input signals using correction parametersstored in EEPROM 544 during manufacture in order to thereby removeundesirable harmonics that could adversely affect position sensing.

A processor 570 is coupled to receive the conditioned channel signalsand is configured to calculate an angle and/or speed of motion (e.g.,rotation) of the target 520. For example, target angle can be computedusing a CORDIC method and target speed can be computed as the derivativeof target angle. For example, using consecutive angle values in time,speed is proportional to (angle_1−angle_0)/delta_time]. A delaycompensator 572 can reduce the effective path latency of the interface518. For example, the calculated speed can be used to correct the anglesignal provided at the output of compensator 572 for the delays insignal path.

Sine and cosine elements 576, 578 can reconstruct sine and cosinedifferential signals that can be provided as interface output signals.The sine and cosine signals thus generated can be converted to analogsignals by respective digital-to-analog converters (DACs) 580, 582.Output drivers 584, 586 can be coupled to receive the analog sine andcosine signals, as shown.

The interface output signals can be provided in one or more of variousformats at one or more connections 592, 594, 596, 598 for coupling toexternal elements and systems (not shown). In the example interface 518,the output signals are provided in a selected one of a quadraturedifferential analog signals (SINP, SINN at connections 592, 594 andCOSP, COSN at connections 596, 598) or an angle position signal providedin a Serial Peripheral Interface (SPI) format. SPI processor 574controls a multiplexer 588 in order to provide interface output signalsaccording to the SPI format or as differential sine and cosine outputsignals. The selection of interface output signal type can be based onuser-programmable parameters stored in EEPROM 544. It will beappreciated that other output signal information such as speed anddirection and other output signal formats are possible, including butnot limited to Pulse Width Modulation (PWM) format, Single Edge NibbleTransmission (SENT) format, Local Interconnect Network (LIN) format, CAN(Controller Area Network) format, and/or an Inter-Integrated Circuit(I²C) format to name a few.

Interface 518 can be provided in the form of an integrated circuit (IC)including one or more semiconductor die and can receive power V_(SUPPLY)502 at a connection 504 for coupling to an on-chip regulator 506 and canhave a ground connection 590. A digital regulator 510 can generate aregulated voltage for powering digital circuitry of the interface and apower-on reset circuit 508 and a level detect circuit 512 can beprovided. A charge pump 582 can be coupled to a memory device, such asan EEPROM 580 for storing operating values and parameters, such asoutput signal format, gain and offset correction coefficients, andharmonic correction parameters as examples.

While the interface 518 may be provided in the illustrated form of an ICwith an analog front end portion and a digital portion, it will beappreciated that the particular delineation of which circuit functionsare implemented in an analog fashion or with digital circuitry andsignals can be varied. Further, some of the illustrated circuitfunctions can be implemented on an interface IC and other circuitry andfunctionality can be implemented on separate circuits (e.g., additionalsubstrates within the same integrated circuit package, or additionalintegrated circuit packages, and/or on circuit boards).

All references cited herein are hereby incorporated herein by referencein their entirety.

Having described preferred embodiments, which serve to illustratevarious concepts, structures and techniques, which are the subject ofthis patent, it will now become apparent that other embodimentsincorporating these concepts, structures and techniques may be used.Accordingly, it is submitted that the scope of the patent should not belimited to the described embodiments but rather should be limited onlyby the spirit and scope of the following claims.

What is claimed is:
 1. A position sensor system configured to sense aposition of a target, comprising: an oscillator configured to generatean oscillation signal having a carrier frequency and a primary phase; aprimary coil coupled to receive the oscillation signal; a secondary coilelectromagnetically coupled to the primary coil and configured togenerate a secondary signal having the carrier frequency and a secondaryphase; a sampling and conversion circuit configured to sample thesecondary signal during sample periods and convert the secondary signalinto a digital signal; a demodulator coupled to receive the digitalsignal and configured to demodulate the digital signal in order togenerate a position signal indicative of the position of the target; aphase detector coupled to receive the position signal and configured todetect an alignment of the secondary phase with respect to the sampleperiods and generate a phase detector output signal indicative ofwhether the secondary phase is aligned with the sample periods; and adelay circuit responsive to the phase detector output signal andconfigured to apply a delay to the sampling and conversion circuit ifthe phase detector output signal indicates that the secondary phase isnot aligned with the sample periods.
 2. The position sensor system ofclaim 1, wherein the demodulator comprises a multiplier configured tomultiply the digital signal by a square-wave signal, wherein thesquare-wave signal has a phase aligned with the primary phase.
 3. Theposition sensor system of claim 2, further comprising a phase-lockedloop configured to generate the square-wave signal.
 4. The positionsensor system of claim 3, wherein the square-wave signal has a frequencyof at least four times the carrier frequency.
 5. The position sensorsystem of claim 1, wherein the phase detector output signal indicatesthat the secondary phase is not aligned with the sample periods if anamplitude of a current sample of the position signal does not match anamplitude of a previous sample of the position signal.
 6. The positionsensor system of claim 1, wherein the secondary coil comprises a firstsecondary coil and a second secondary coil, wherein the first secondarycoil is configured to generate a first secondary signal containing firstamplitude modulated information and the second secondary coil isconfigured to generate a second secondary signal containing secondamplitude modulated information that is ninety-degrees out of phase withrespect to the first amplitude modulated information.
 7. An interfacecircuit for a position sensor system including an oscillator generatingan oscillation signal having a carrier frequency and a primary phase, aprimary coil responsive to the oscillation signal, and a secondary coilelectromagnetically coupled to the primary coil by a target andconfigured to generate a secondary signal having the carrier frequencyand a secondary phase, the interface circuit comprising: a sampling andconversion circuit configured to sample the secondary signal duringsample periods and convert the secondary signal into a digital signal; ademodulator coupled to receive the digital signal and configured todemodulate the digital signal in order to generate a position signalindicative of a position of the target; a phase detector coupled toreceive the position signal and configured to detect an alignment of thesecondary phase with respect to the sample periods and generate a phasedetector output signal indicative of whether the secondary phase isaligned with the sample periods; and a delay circuit responsive to thephase detector output signal and configured to apply a delay to thesampling and conversion circuit if the phase detector output signalindicates that the secondary phase is not aligned with the sampleperiods.
 8. The position sensor system of claim 7, wherein thedemodulator comprises a multiplier configured to multiply the digitalsignal by a square-wave signal, wherein the square-wave signal has aphase aligned with the primary phase.
 9. The position sensor system ofclaim 8, further comprising a phase-locked loop configured to generatethe square-wave signal.
 10. The position sensor system of claim 9,wherein the square-wave signal has a frequency of at least four timesthe carrier frequency.
 11. The position sensor system of claim 7,wherein the phase detector output signal indicates that the secondaryphase is not aligned with the sample periods if an amplitude of acurrent sample of the position signal does not match an amplitude of aprevious sample of the position signal.
 12. The position sensor systemof claim 7, wherein the secondary coil comprises a first secondary coiland a second secondary coil, wherein the first secondary coil isconfigured to generate a first secondary signal containing firstamplitude modulated information and the second secondary coil isconfigured to generate a second secondary signal containing secondamplitude modulated information that is ninety-degrees out of phase withrespect to the first amplitude modulated information.
 13. In a positionsensor system having an oscillator generating an oscillation signalhaving a carrier frequency and a primary phase, a primary coilresponsive to the oscillation signal, and a secondary coilelectromagnetically coupled to the primary coil and configured togenerate a secondary signal having the carrier frequency and a secondaryphase, a method for detecting a position of a target, the methodcomprising: a sampling the secondary signal during sample periods;converting the sampled secondary signal into a digital signal;demodulating the digital signal to generate a position signal indicativeof the position of the target; detecting an alignment of the secondaryphase of the position signal with respect to the sample periods togenerate a phase detector output signal indicative of whether thesecondary phase is aligned with the sample periods; and applying a delayto the sampling and converting of the secondary signal if the secondaryphase is not aligned with the sample periods.
 14. The method of claim13, wherein demodulating the digital signal comprises multiplying thedigital signal by a square-wave signal, wherein the square-wave signalhas a phase aligned with the primary phase.
 15. The method of claim 14,further comprising generating the square-wave signal with a phase-lockedloop.
 16. The method of claim 15, wherein generating the square-wavesignal comprises generating the square-wave signal with a frequency ofat least four times the carrier frequency.
 17. The method of claim 13,wherein the phase detector output signal indicates that the secondaryphase is not aligned with the sample periods if an amplitude of acurrent sample of the position signal does not match an amplitude of aprevious sample of the position signal.
 18. An interface circuit for aposition sensor system including an oscillator generating an oscillationsignal having a carrier frequency and a primary phase, a primary coilresponsive to the oscillation signal, and a secondary coilelectromagnetically coupled to the primary coil by a target andconfigured to generate a secondary signal having the carrier frequencyand a secondary phase, the interface circuit comprising: means forsampling the secondary signal during sample periods and converting thesecondary signal into a digital signal; means for processing the digitalsignal to generate a position signal indicative of a position of thetarget; means for detecting an alignment of the secondary phase withrespect to the sample periods based on the position signal; and meansfor applying a delay to the sampling and converting means if thesecondary phase is not aligned with the sample periods.
 19. Theinterface circuit of claim 18, wherein the alignment detecting meanscomprises means for determining if an amplitude of a current sample ofthe position signal matches an amplitude of a previous sample of theposition signal.